How can I see all packages that depend on a certain package with PIP?

Update (2021):

Since pip version 10 you can do:

pkg=httplib2
pip show $pkg | grep ^Required-by

or for bash

pkg=httplib2
grep ^Required-by <(pip show $pkg)

so you could create an alias like:

alias pyreq='pip show $pkg | grep ^Required-by'

and querying by:

pkg=httplib2 pyreq

which should give (for ubuntu):

Required-by: lazr.restfulclient, launchpadlib

Original:

Quite straightforward:

pip show <insert_package_name_here>| grep ^Requires

Or the other way around: (sorry i got it wrong!)

for NAME in $(pip freeze | cut -d= -f1); do REQ=$(pip show $NAME| grep Requires); if [[ "$REQ" =~ "$REQUIRES" ]]; then echo $REQ;echo "Package: $NAME"; echo "---" ; fi;  done

before that set your search-string with:

REQUIRES=django

essentially you have to go through the whole list and query for every single one. That may take some time.

Edit:
Also it does only work on installed packages, I don’t see pip providing dependencies on not installed packages.